Effects of Strain Rate on Delamination Fracture Toughness of Graphite/Epoxy

Abstract

The objective of this paper is to evaluate various experimental techniques and analysis methods for the characterization of interlaminar fracture toughness, and to determine the effects of strain rate on that property for a graphite/epoxy composite. Mode I interlaminar fracture was investigated by means of a double-cantilever beam (DCB) specimen for AS-4/3501-6 graphite/epoxy. Hinged tabs were used to insure unrestrained rotation at the free ends. Specimens were loaded at quasi-static deflection rates of up to 8.5 mm/s (20 in./min) corresponding to crack extension rates of over 51 mm/s (2 in./s). Crack extension was monitored by means of strain gages mounted on the surface of the specimen, or a conductive-paint circuit attached to the edge of the DCB specimen. Continuous records were obtained of load, deflection, and crack extension for determination of the strain energy release rate. The latter was expressed as a power law of the crack extension velocity. Results indicate that the strain energy release rate increases with crack velocity by up to 28% for the range of rates considered here.

Mixed-mode bending method for delamination testing

“…17 The beam theory equations for strain energy release rate can be further improved by accounting for the shear deformation energy associated with bending. Adding the shear deformation component of strain energy release rate 18 to Eq. (7) Assuming the unidirectional composite specimens used in the present study are transversely isotropic, the shear modulus 613 in these two equations can be replaced by G12.…”

Development of a methodology for determination of interface fracture toughness of laminate composites—the 0°/90° pair

“…Most studies on the fracture toughness of fiber composite materials have focused on unidirectional composites (Jurf and Pipes, 1982;Whitney et al, 1982;Aliyu and Daniel, 1985;Gillespie et al, 1987;Davies et al, 1990;Hashemi et al, 1990;Reeder and Crews, 1990;Yoon and Hong, 1990;Kinloch et al, 1993;Bansal and Kumosa, 1995;Zhao et al, 1995;Liu et al, 1997;Rikards et al, 1998, for example). Liu et al (1997) employed the Brazilian disk specimen to determine the fracture toughness of uniaxial laminate composites with a crack in the direction of the fibers, as well as perpendicular to them.…”

A critical analysis of interface constitutive models for the simulation of delamination in composites and failure of adhesive bonds

“…A total of 290 solid-shell elements are taken for the double cantilever [Fiolka 2007]. Figure 5, left, displays the experimental data from [Aliyu and Daniel 1985] and the analytical solution from [Mi et al 1998] together with the finite element simulation. The numerical and the experimental results are identical until the load peak is reached, where the crack begins to increase.…”